Pig systems for transporting liquid or pasty substances are widespread in the art, in particular in coating technology, where they are primarily used in supply units for application devices. There they are used, inter alia, for the transport of paint between paint-carrying loop lines of the spray booth and the application device.
Pigs are subject to natural wear and tear, so that, after a certain operating time, they become uptight and leaks occur along them. They must then be replaced. This should be able to be done in as short a time as possible and, if need be, also automatically, in order that costly downtimes of the plant are as far as possible avoided. In the pig system which is described in DE 10 2004 037 247 B4 and corresponds to the type stated in the introduction, there is provided a pig changing station, which is disposed outside of a pig station and contains a multiplicity of positions in which pigs, new or defective, can be stored. This external pig changing station is connected to the pig station by a line or a hose. Normally, the pig channel in this pig station is closed off by a stopper, against which the single pig moving in the actual pig system abuts. For the exchange of this pig, this stopper is removed by an appropriate mechanism and the hose leading to the pig changing station is connected up to the pig channel, so that now the defective pig is moved out and can be conveyed into a position of the pig changing station. A new, functional pig is thereupon introduced in the reverse direction into the pig channel of the pig station and the pig channel is closed off again by the stopper. In this way, a great number of pigs can be introduced into the pig system, which ensures very high service lives. However, this mechanism is very complicated and the times which are required for the pig change are not wholly insignificant.